I kept hoping that the Dad crush thing was just Hiro's interpretation but damn it's pretty blatant these chapters, isn't it? Poor kid.
So far, she's crawled into Hiro's bed and gone to sleep hugging her, twice, and then there was the whole lap pillow. I was going to say Hiro should take the hint already, but she may not be the only one.
I also have two new theories, one of which is more plausible than the other.
First, the dreams Hiro keeps happening are actually distorted memories of her mother and father interacting, with Karin taking her mother's place, hence her father's younger look.
The second is less of a theory, but I'm wondering if Hiro might not be the only one in the family who's a bit queer, since I'm now hoping for her father X Yukio, the close friend who goes out of his way to come over and bring wagyu beef to a barbecue and who comes over so often he's no longer considered a guess.